In a1-a3 are three keywords, a1 and a3 with search volume, a2 - without. Firstly we test the keyword one after one: the first has search volume data, the second hasn’t, the third has it again.

Now we test the list of the first and third keyword (a1 and a3, those with keyword data) - the data we get are correct, exactly as in Keyword Planner GUI.

Then we test all three keywords: the first with SV, the second without and the third with sv: the results is weird. The first keyword with SV gets correct data, the second keyword without search volume gets the data of the third keyword, the third keyword disappears.